It has become increasingly important to eliminate the features associated with a ballistic trajectory ordinarily followed by rockets and other jet-propelled projectiles, by forming the projectiles as spherical spin-stabilized missiles. The term "spherical" herein and in the claims hereof is being used in a generic sense to mean line-of-sight projectiles or missiles. For instance, in the exemplary embodiment herein, the missile is spherical only in the forward half of the missile, the aft half being substantially conical in shape.
The spherical missile spins about an axis upwardly inclined relative to the intended straight-line path of flight and aligned with the missile propulsion thrust axis. The missile is released following ignition or activation of the propulsion system within the missile. The propulsion is effected by the reaction of the exhaust jet of, for example, a rocket motor housed within the spherical missile shell. Such spherical spin-stabilized missiles often are provided in conjunction with attachments secured to the front end of an assault weapon such as a rifle.
Such spin-stabilized, spherical, self-propelled missiles experience difficulties in achieving missile spin axis alignment during attainment of desired rotational speed and in coordinating the spinning and release of the missile. Release of the missile prior to attainment of adequate rotational speed can result in unstable flight. Delay of release after attainment of adequate rotational speed can result in a loss of propulsion range.
Consequently, attempts have been made to provide means for temporarily restraining and automatically releasing a spin-stabilized self-propelled spherical missile during spin-up Some such attempts are shown in U.S. Pat. Nos. 3,245,350 to J. A. Kelly, dated Apr. 12, 1966; 3,554,078 to Joseph S. Horvath, dated Jan. 12, 1971; 4,395,836 to Baker et al., dated Aug. 2, 1983; and 4,403,435 to Baker et al., dated Sept. 13, 1983, the latter two patents being assigned to the assignee of this invention. These patents represent a continuing effort to provide workable spherical spin-stabilized missiles. Generally, a fusible link temporarily restrains and automatically releases the spherical missile during spin-up. Hot missile rocket exhaust gas weakens, by heating, and melts the fusible link which, prior to weakening by softening or melting, secures the missile to a rotary support means. Baker U.S. Pat. No. 4,395,836 shows a novel unitary nozzle member having fusible joint means formed integrally therewith, between the missile and the rotary support means. Baker U.S. Pat. No. 4,403,435 shows an improved nozzle assembly including projectile support means having open-ended receptacle means out of which fore and aft sections of the nozzle can move on fusing and separation of the fusible joint means. This patent also shows an improved register section for the missile or nozzle to improve alignment of the missile with the spin axis during initial separation of the fusible joint means.
A somewhat radical departure from the prior art is shown in copending application Ser. No. 195,657, filed May 18, 1988, and assigned to the assignee of the present invention. That invention is directed to a projectile release mechanism wherein a mass is caused to be urged or propelled rearwardly by the gases of the missile or other suitable stored energy mechanism to strike an abutment means on the turbine or rotary means for the missile to cause the rotary means, in its receptacle, to move rapidly away from the missile after separation of the fusible joint means. This allows positive missile retention by the launch system rotary means during coupling fusing and therefore eliminates pointing error tip off forces initiated during the coupling fusing process of prior apparatus. That invention represents a vast improvement in the prior art, in that the missile separates from its turbine assembly in less than 0.5 msec., compared to the 10 msec separation period encountered in earlier designs in the art. This huge reduction in separation time minimizes the transfer of separate impulse forces from the turbine coupling and assembly to the projectile.
However, still further problems have been encountered designing such spin-stabilized self-propelled missile systems, a condition which has been termed a "repointing condition" which is caused by projectile construction static and dynamic unbalances. In other words, the axis of the turbine assembly or rotary missile support means attempts to control the system control spin axis, while the relatively large missile segment of the system attempts to create its own axis of rotation. If these axes are not colinear, the missile tends to wobble during spinup and jump to an unaimed heading upon release. For ease of understanding, it is as if a common screwdriver was bent and rapidly rotated when in use. The missile ends up being repointed to an angle generally equal to one-half of the misalignment angle between the axis of the rotary support means (spin axis) and the axis of rotation or geometric axis of the missile. This is what is termed a "repointing condition".
Heretofore, attempts to overcome the repointing condition were limited to dynamic balancing of the projectile itself. In other words, weight means were applied to the missile somewhat similar to the common balancing of a vehicle tire. This approach yielded usable accuracy results, but it is impractical to consider live warhead projectile dynamic balancing in a production environment.
The present invention is directed, generally, to a producibility sensitive alternative to dynamic balancing by a physical determination of the alignment of the spin axis of the rotary support means and the geometric axis of the projectile, and correcting any misalignment in a manner compatible with a production environment.